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exam03 - Minhat Mohammad Haz Exam 3 Due 10:00 am Inst Kohl...

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Minhat, Mohammad Haz – Exam 3 – Due: Nov 10 2006, 10:00 am – Inst: Kohl 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. pH= -log[H3O+] pOH= -log[OH-] pKw=14 HH Equations pH = pKa + log([salt]/[acid]) pOH= pKb + log([salt]/[base]) 001 (part 1 of 1) 4 points The hydronium ion (H + ) concentration of 0.15 M acetic acid is 6.3 × 10 - 4 mol/L. What is the pH of the solution? 1. 4.2 2. 10.6 3. 0.82 4. 3.2 correct 5. 3.0 6. 5.7 7. 8.2 8. 1.4 Explanation: [H + ] = 6 . 3 × 10 - 4 mol/L By definition, pH = - log(hydrogen ion molarity) = - log(6 . 3 × 10 - 4 ) = 3 . 2 002 (part 1 of 1) 4 points Mixing 50 ml of 0 . 010 M Ba(OH) 2 and 150 mL of 0.010 M HNO 3 will result in a solution with what pH? 1. 2.60 correct 2. 11.70 3. 0.30 4. 13.70 5. 2.30 Explanation: V HNO 3 = 150 mL V Ba(OH) 2 = 50 mL [HNO 3 ] = 0.010 M [Ba(OH) 2 ] = 0.010 M Initially(ini): n Ba(OH) 2 = 50 × 0 . 010 = 0 . 5 mmol n HNO 3 = 150 × 0 . 010 = 1 . 5 mmol Ba(OH) 2 + 2 HNO 3 Ba 2+ +2 NO - 3 +2 H 2 O ini 0 . 5 1 . 5 0 0 Δ - 0 . 5 - 1 0 . 5 1 fin 0 0 . 5 0 . 5 1 HNO 3 is a strong acid and Ba 2+ and NO - 3 are spectator ions. Total volume = 200 mL [H 3 O + ] = 0 . 5 mmol 200 mL = 0 . 0025 M pH = - log(0 . 0025) = 2 . 60206 003 (part 1 of 1) 4 points Consider the ionization constants cyanic acid (HOCN) : K a = 3 . 5 × 10 - 4 ; ammonia (NH 3 ) : K b = 1 . 8 × 10 - 5 . A solution of ammonium cyanate (NH 4 OCN) is 1. acidic, because the cation and the anion hydrolyze to the same extent. 2. neutral, because NH 4 OCN is a weak base/weak acid salt. 3. acidic, because the anion hydrolyzes to a greater extent than the cation. 4. neutral, because the cation and the anion hydrolyze to the same extent. 5. neutral, because the cation hydrolyzes to a greater extent than the anion. 6. basic, because the anion hydrolyzes to a greater extent than the cation.
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Minhat, Mohammad Haz – Exam 3 – Due: Nov 10 2006, 10:00 am – Inst: Kohl 2 7. acidic, because the cation hydrolyzes to a greater extent than the anion. correct 8. basic, because the cation and the anion hydrolyze to the same extent. 9. neutral, because the anion hydrolyzes to a greater extent than the cation. 10. basic, because the cation hydrolyzes to a greater extent than the anion. Explanation: 004 (part 1 of 1) 4 points The solubility product constant of Ag 2 CrO 4 is 9 . 0 × 10 - 12 . What is the molar solubility of Ag 2 CrO 4 in a solution in which the silver ion concentration is maintained at 2 . 0 × 10 - 3 M by addition of AgNO 3 ? 1. 4 . 0 × 10 - 3 2. 5 . 6 × 10 - 7 3. 1 . 3 × 10 - 4 4. 2 . 3 × 10 - 6 correct 5. 4 . 5 × 10 - 9 Explanation: 005 (part 1 of 1) 4 points How much acetic acid ( K a = 1 . 8 × 10 - 5 ) must be used to prepare a liter of solution having a pH of 2.75? 1. 5.69 moles 2. 9.88 moles 3. 0.178 moles correct 4. 0.435 moles 5. 0.0101 moles Explanation: pH = - log[H + ] = 2 . 75 so [H + ] = log - 1 ( - 2 . 75) = 1 . 778 × 10 - 3 mol HA * ) H + + A - Subsitute [H + ] = [A - ] = 1 . 778 × 10 - 3 into the equation for K a : K a = [H + ][A - ] [HA] [HA] = [H + ][A - ] K a = ( 1 . 778 × 10 - 3 ) 2 1 . 8 × 10 - 5 0 . 178 mol 006 (part 1 of 1) 4 points Suppose that a sample of pure water is satu- rated with gaseous CO 2 to form a solution of carbonic acid. Which response has the follow- ing species arranged in the order of decreasing concentrations at equilibrium (from highest concentration to lowest concentration)?
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